1. Field of the Invention
The present invention relates to an air conditioner including a plurality of positive temperature coefficient (PTC) heaters.
2. Description of Related Art
A conventional air conditioner is disclosed in Japanese Patent Application Laid-open No. Hei 08-152179. The air conditioner has an integrated structure in which an indoor unit to be placed indoors is disposed in the front and an outdoor unit to be placed outdoors is disposed in the rear. In the outdoor unit, there are disposed a compressor for operating the refrigeration cycle and an outdoor heat exchanger connected to the compressor. The indoor unit has an inlet and an outlet opened therein. Inside the indoor unit, there are disposed an indoor heat exchanger connected to the compressor via a refrigerant pipe, and a heating portion including a plurality of PTC heaters.
When the temperature of the PTC heater exceeds the Curie point, the PTC heater increases in resistance, and hence a current value and a heating amount thereof are reduced. Accordingly, a stable amount of heating in a heating portion is obtained, which makes it easy to generate warm air of a predetermined temperature while preventing overheating. In this case, the resistance of the PTC heater changes depending on ambient temperature or an air flow rate. Therefore, predetermined control is carried out so as not to exceed power capacity, by monitoring a current value of the heating portion from the time of start-up of the PTC heater, when the resistance is low, until the PTC heater enters a stable state with high resistance.
When starting cooling operation, the refrigeration cycle is operated by the drive of the compressor, and the indoor heat exchanger serves as an evaporator on the low temperature side in the refrigeration cycle while the outdoor heat exchanger serves as a condenser on the high temperature side in the refrigeration cycle. The air in a room flows into the indoor unit from the inlet to be subjected to heat exchange with the indoor heat exchanger so that the air thus cooled is delivered to the room from the outlet. This way, cooling in the room is performed.
When starting heating operation, the refrigeration cycle is operated by the drive of the compressor, and the indoor heat exchanger serves as a condenser on the high temperature side in the refrigeration cycle while the outdoor heat exchanger serves as an evaporator on the low temperature side in the refrigeration cycle. The air in a room flows into the indoor unit from the inlet to be subjected to heat exchange with the indoor heat exchanger and is thereby heated. The air flowing into the indoor unit is further heated by the drive of the heating portion. The air thus heated is delivered to the room from the outlet, to thereby perform heating in the room.
The heating portion has different power capacity depending on where to install the air conditioner. At the installation, the number of the PTC heaters to be connected is adjusted according to a current value of the PTC heater in the stable state. In this case, depending on the number of the PTC heaters in a connected state, different control is carried out on the heating portion from the start-up until the stable state. Specifically, when the number of the PTC heaters in the connected state is large, the power capacity is high and hence the heating portion is controlled with an upper limit of the current value set high. On the other hand, when the number of the PTC heaters in the connected state is small, the power capacity is low and hence the heating portion is controlled with the upper limit of the current value set low. Therefore, it is necessary to detect the number of the PTC heaters in the connected state.
In a case where the number of the PTC heaters to be connected is set by an installation worker, an erroneous input is liable to happen. As a countermeasure, a plurality of current detecting circuits are provided correspondingly to the PTC heaters so as to detect the number of the PTC heaters in the connected state based on respective current values of the PTC heaters.
However, the current detecting circuit is expensive, leading to a problem of high cost of the air conditioner. Further, the current detecting circuit requires a large space for parts on a control board, which increases the size of the control board, leading to another problem of increased size of the air conditioner.